Smell And Taste DSA

Question 1

Odorant receptors (OR) are located on the cilia that protrude into the mucus layer. How many ORs do humans express? How many odorants are capable of activating each receptor?

Answer 1

Humans express 350 different ORs

Multiple odorants can activate each receptor

Question 2

Describe the biochemistry of the odorant receptors

Answer 2

ORs are G-protein coupled receptors that create cAMP to open a cyclic-nucleotide gated ion channel
Like Gs, but is Golf

Question 3

What happens if the odorant persists?

Answer 3

Sensitivity of channel to cyclic AMP is reduced, decreasing Na+ and Ca++ entry.
A smaller generator potential results, reducing the probability of an action potential in the axon

Question 4

Each olfactory neuron expresses the same odorant receptor on ___ of its cilia.

Answer 4

ALL

Question 5

Describe the location of odorant receptors on olfactory epithelium

Answer 5

Although entire olfactory epithelium expresses odorant receptors, different ORs are located to different parts of the epithelium, but not equally between these areas.
Each zone in the epithelium has a different receptor type that predominates, even though many different receptor types are present in each zone

Question 6

Describe odorant and odor

Answer 6

Each odorant activates different combinations of odorant receptors to produce its characteristic odor
Odorant concentration changes the perceived smell (at higher conc., odorant starts to bind to receptors with a lower affinity for the odorant in addition to the receptors with a higher affinity)

Question 7

Describe trace amine-associated receptors (TAARs)

Answer 7

Activation of TAARs produces physiological/endocrine responses to pheromones
Many chemicals that activate TAARs are found in greatest concentration in urine from males of species being studied

Question 8

What cells are not activated directly by olfactory cells?

Answer 8

Granule cells

Question 9

What are the kinds of post-synaptic neurons in the glomeruli, and where do they go?

Answer 9

Mitral cells
Tufted cells
The axons from these will go to olfactory cortex

Periglomerular cells
Axons will remain in olfactory bulb

Question 10

What do the axons from the olfactory neurons expressing the same odorant receptor do?

Answer 10

Converge on two glomeruli (one medial, one lateral) located in the ipsilateral olfactory bulb

Question 11

What do periglomerular cells do?

Answer 11

Release GABA at their synaptic contacts with other glomeruli and inhibit the activity from those glomeruli
Since these glomeruli are likely related odorants, this means that the odorant producing the strongest stimulation will suppress the input from other glomeruli that weren’t as strongly activated and improve the signal specificity in the brain

Question 12

What do granular cells do?

Answer 12

Release GABA at their synaptic contacts, but they synapse with mitral and tufted cells.
Believed that they also work to increase the specificity of message going to the olfactory cortex

Question 13

What is the first possible synapse in olfactory cortex?

Answer 13

Anterior olfactory nucleus
These synapses relay the information to the contralateral side
Axons also continue on the ipsilateral side

Question 14

What does the entorhinal cortex do?

Answer 14

Projects to hippocampus, which is important in memory formation
Olfactory input facilitates both memory formation and recall

Question 15

What does the piriform cortex do?

Answer 15

Projects to lateral hypothalamus, which is important in control of appetite
Olfactory inputs can influence appetite

Also projects to medial orbitofrontal cortex (via thalamus) to provide information that will be used to identify the flavor of foods

Question 16

What does the olfactory cortex do to modify receptor responses to odorants?

Answer 16

Sends input back to olfactory bulb/olfactory epithelium

Question 17

How are sour tastes produced?

Answer 17

When hydrogen ion enters taste bud via hydrogen-ion channel

Question 18

How are salty tastes produced?

Answer 18

When sodium or calcium ion enter the taste bud via a sodium or calcium channel

Question 19

How is the umami (savory) taste produced?

Answer 19

The receptor is a metabotropic glutamate receptor activated by amino acid glutamate

Question 20

How are sweet and bitter tastes produced?

Answer 20

They use second messenger systems to depolarize the cell, but they are not directly related to metabotropic receptors that detect umami

Question 21

Describe gustatory inputs

Answer 21

Inputs travel a straight-forward path to brain
There are synapses in the NTS, thalamus, and gustatory cortex (includes anterior insular cortex)
From the thalamus, the axons go to cortex and to lateral hypothalamus. This input has significant impact on appetite.

Question 22

What is the gustatory cortex involved with?

Answer 22

Seems to be strongly involved in identifying the basic taste and innate responses such as attraction to sweet tastes or aversion to bitter tastes

Question 23

What does the perception of flavor require?

Answer 23

Gustatory input from gustatory cortex
Olfactory input from olfactory cortex (especially piriform cortex)
Somatosensory information from mouth

Neurons from all three areas of cortex send axons to lateral posterior orbitofrontal cortex to produce sensation of flavor and appreciation of food

Question 24

What is the clinical relevance of the high turnover rate of odorant and taste receptors?

Answer 24

The ability to smell and taste changes with age and a result of certain pharmacological treatments.
There is an age-specific decline in ability to detect mercaptan that is added to natural gas
Changed perceptions about what smells or tastes good can profoundly affect appetite and food preferences